Surgical procedures requiring cutting of tissue can cause bleeding at the site of the cutting. Before surgeons had the means to control bleeding many surgical procedures were quite difficult to perform because of excessive blood loss. Hemostasis is even more crucial in endoscopic or laparoscopic surgery where if the bleeding is not kept under control, the laparoscopy must be abandoned and the patient's body cut to perform open surgery so that inaccessible bleeding may be controlled.
Thus, various techniques have been adapted to control bleeding with varying degrees of success such as, for example, suturing, applying clips to blood vessels, and stapling, as well as electrocautery and other thermogenic techniques. Advances in tissue joining, tissue repair and wound closure also have permitted surgical procedures previously not possible or too risky.
Initially, suturing was one of the primary means for providing hemostasis and joining tissue. Before other hemostatic and tissue repair means were introduced, surgeons had to spend a great deal of time sewing the tissue of patients back together.
Surgical clips were introduced as a means to close off blood vessels, particularly when cutting highly vascularized tissue. Application of surgical clips, however, can be cumbersome in certain procedures. The vessels must be identified. Then a clip must be individually applied on both sides of the intended cut of each identified vessel. Also, it may be difficult to find some vessels, particularly where the vessel is surrounded by fatty tissue.
Surgical staplers have been effective in decreasing the amount of time it takes to fasten tissue together. There are various types of surgical staplers. Staplers have been used for tissue joining, and to provide hemostasis in conjunction with tissue cutting. Such devices include, for example, linear and circular cutting and stapling instruments. Typically, a linear cutter has parallel rows of staples with a slot for a cutting means to travel between the rows of staples. This type of surgical stapler secures tissue for improved cutting, joins layers of tissue, and provides hemostasis by applying parallel rows of staples to layers of surrounding tissue as the cutting means cuts between the parallel rows. These types of cutting and stapling devices have been used successfully in procedures involving fleshy tissue such as muscle or bowel, particularly in bowel resection procedures. Circular cutting and stapling devices have successfully been used, for example, in anastomotic procedures where a lumen is rejoined. However, the results with cutting and stapling devices have been less than optimum where the procedure involves cutting highly vascularized tissue, such as mesentery or adnexa, which are prone to having hemostasis problems.
Electrocautery devices have also been used for effecting hemostasis. Monopolar devices utilize one electrode associated with a cutting or cauterizing instrument and a remote return electrode, usually adhered externally to the patient. More recently, bipolar instruments have been used because the cauterizing current is generally limited to tissue between two electrodes of the instrument.
Bipolar forceps have been used for cutting and/or coagulation in various procedures. For example, bipolar forceps have been used in sterilization procedures where the fallopian tubes are sealed off. Generally, bipolar forceps grasp tissue between two poles and apply electrical current through the grasped tissue. Bipolar forceps, however, have certain drawbacks, some of which include the tendency of the current to arc between poles when tissue is thin or the forceps to short when the poles of the forceps touch. The use of forceps for coagulation is also very technique dependent and the forceps are not adapted to simultaneously cauterize a larger area of tissue.
Bipolar scissors have been disclosed where two scissors blades act as two electrodes having insulated shearing surfaces. This device mechanically cuts tissue as coagulating electrical current is delivered to tissue in the current path. Bipolar scissors are also highly technique dependent in their use.
In prior devices, such as the device described in U.S. Pat. No. 5,403,312, electrosurgical energy has been delivered to biologic tissue in order to create a region of coagulation, as, for example, on either side of an incision, thus preventing blood and other bodily fluids from leaking out of the incision. In such a device, if tissue grasped by the jaws is compressed too much by applying excessive pressure to the region of coagulation, the tissue grasped by the end effector may be torn or crushed. If the tissue is not compressed enough because to little pressure is applied to the region of coagulation, the tissue in the region of coagulation may not be not effectively or uniformly cauterized because fluid (e.g. blood) could remain in the region of cauterization. In prior art devices, the surgeon has used tactile feedback and visual clues to determine the amount of pressure to apply to the region in order to obtain optimum coagulation. In instruments wherein the region of coagulation is partially or fully obscured, either by the end effector or by tissue, and is, therefore, not visible to the surgeon, it is particularly difficult for the surgeon to ensure that the appropriate pressure is being applied by the end effectors to ensure proper coagulation. It would, therefore, be advantageous to develop an electrosurgical instrument wherein the surgeon is not required to adjust the pressure applied by the end effector prior to applying electrosurgical energy to tissue in the region of coagulation. It would further be advantageous to design an instrument wherein the pressure applied to the tissue prior to coagulation is within a predetermined range.
One known method of varying the pressure applied to the tissue by the jaws of the end effector involves varying the gap between the jaws depending upon the tissue being grasped. However, such an arrangement would necessitate the use of different instruments, different end effectors or different staple cartridges depending upon the tissue being grasped. It would, therefore, be advantageous to design an instrument wherein the pressure applied by the end effector would vary with the thickness and makeup of the tissue being grasped.
Non electrosurgical endocutters such as those described in U.S. Pat. No. 5,597,107, employ a relatively stiff lower jaw member which includes a staple cartridge in conjunction with a more flexible upper member which acts as an anvil against which the staples are formed. In such instruments, the anvil is generally manufactured to be as stiff as possible, within the limits of size, materials and other design considerations and the spring rate of such an anvil may be, for example, in the range of 350-450 pounds per inch. A stiff anvil helps to ensure that the staples form properly when the instrument is fired. Spring rate, in terms of tissue compression forces in conventional staplers with gap spacing pins, is used in conjunction with the gap pin to create and maintain a minimum gap between the staple cartridge and the anvil, setting the height of the formed staple. Therefore, the designers of conventional stapling instruments with gap spacing pins are primarily interested in the formation of a simple beam with consistent gap to form consistent staples. In other designs, the gap pin is not used and the anvil is designed with sufficient stiffness to facilitate the formation of tissue. It would, therefore, be advantageous to design an electrosurgical instrument where the spring rate of the anvil is sufficiently stiff for the formation of staples while exerting a pressure in a range which facilitates the proper cauterization of tissue.